A virtual disk image is an electronic file which a virtual machine monitor (VMM) interprets as a physical disk. Common formats for virtual disk images include .VMDK, .VHD, and .VDI.
An administrator of virtual machine (VM) platforms may wish to copy a virtual disk image from one place (or physical location) to another. For example, the administrator may wish to maintain copies of the same virtual disk image at different sites for disaster recovery purposes. As another example, the administrator may wish to backup a virtual disk image, i.e., take a VM snapshot of a virtual disk image. As yet another example, the administrator may wish to duplicate VMs on multiple VM farms from a non-writeable virtual disk image called a “golden image”.
To copy a virtual disk image from a first device to a second device, the administrator initially makes sure that the second device has enough physical storage space to hold the virtual disk image, and that a reliable network path exists between the first device and the second device. Next, the administrator moves a complete copy of the virtual disk image from the first device to the second device through the network path until the complete copy of the virtual disk image has been written safely to the physical storage space of the second device.